Adhesively laminated flexible webs

ABSTRACT

THIS INVENTION PROVIDES A LAMINATED WEB COMPRISING A LAMINA OF PAPER TISSUE AND ANOTHER FLEXIBLE LAMINA ADHESIVELY SECURED THERETO BY FILAMENTS OF ADHESIVE FINE ENOUGH TO PRECLUDE THEM FROM OBVIOUSLY AFFECTING THE PROPERTIES OF THE COMBINED LAMINA.

United States Patent C ADHESIVELY LAMINATED FLEXIBLE WEISS Leo M. Germain, Shawinigan, Quebec, Canada, assignor to Gulf Oil Canada Limited, Toronto, Ontario, Canada Original application Oct. 21, 1968, Ser. No. 769,243, now

Patent No. 3,629,027. Divided and this application Jan.

25, 1971, Ser. No. 109,718

Int. Cl. B32b 7/14 US. Cl. 161148 3 Claims ABSTRACT OF THE DISCLOSURE This invention provides a laminated web comprising a lamina of paper tissue and another flexible lamina adhesively secured thereto by filaments of adhesive fine enough to preclude them from obviously affecting the properties of the combined lamina.

RELATED APPLICATION This application is a division of application Ser. No. 769,243, filed Oct. 21, 1968, now US. Pat. 3,629,027, and is directed to the novel laminated paper products disclosed therein by the following disclosure.

This invention relates to methods and apparatus for applying adhesive to a substrate and more particularly to methods and apparatus for applying adhesive, in the form of fine filaments of softened thermoplastic material, to a flexible web, especially a fragile web, e.g. paper tissue, which is immediately secured by the adhesive to another web to form a laminated structure.

It is well known to use thermoplastic resinous materials as adhesives and also Well known to form thermoplastic resinous materials into filaments or threads by spinning from solvent solutions of the materials or by dry spinning (extruding) the materials from the molten state. Both the foregoing spinning methods have been used extensively to prepare long continuous filaments. In US. Pat. 2,385,358 and Canadian Pat. 454,159 of A. W. Hanson there are disclosed methods for preparing and recovering relatively short fine fibers which are drawn from a thin layer or film of fiber-forming material in the liquid or semi-liquid state and caused to set or harden by treatment appropriate to the fiber-forming material, then collected or harvested for further processing by the usual drawing and spinning operations as employed with natural fibers.

The present invention is concerned with the formation of tacky short fine adhesive fibers or filaments of thermoplastic material by methods such as disclosed in the foregoing patents for fiber formation, and application of the filaments to a flexible substrate before they have set or hardened whereby the filaments can adhesively secure the substrate to another material to which it is laminated.

The invention thus comprises a process for adhesively securing a flexible web as a lamina to another flexible web with a thermoplastic resin adhesive which process comprises:

(1) applying a coating of viscous liquid thermoplastic fiber-forming adhesive material ,to at least one of a pair of moving surfaces to establish between them a quantity of the material which is in contact with each of them,

(2) continuously moving each of the surfaces in cyclic motion so that the segments of the surfaces, in contact with the material between the surfaces, are drawing away from one another, the speed of cyclic motion being sufiicient to form fine tacky filaments of viscous liquid thermoplastic adhesive material between the segments as they separate,

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(3) passing a flexible continuous web in proximity to the material between the surfaces on a line which intercepts at least some of the filaments formed from the adhesive material so that tacky filaments are deposited on the web,

(4) laminating a second flexible continuous web to the first web by passing them into contact with one another with the deposited adhesive filaments between them before filaments can set or hardened, and

(5) setting the filaments to form an adhesive bond between the webs.

The invention further consists of apparatus for adhesively laminating a long flexible first Web of material to a second long flexible web, comprising (a) a pair of counter-rotating parallel rollers mounted to maintain, in a gap between them, a quantity of viscous liquid thermoplastic fiber-forming adhesive material,

(b) a third rotating roll mounted parallel to the counter-rotating rolls with its surface in proximity to the outside common tangent of the counter-rotating rolls whereby it intercepts filaments of viscous liquid thermoplastic adhesive formed by counter-rotation of the rollers with the adhesive between them.

(c) means to feed the flexible first web lengthwise continuously over a segment of the curved surface of the third rotating roll where it intercepts filaments of adhesive, whereby the tacky filaments are deposited on the surface of the first web,

((1) means to feed the second web continuously in laminar relation to the first web against the surface on which the filaments of adhesive are deposited While said filaments are still tacky, and

(e) means to hold the two webs in laminar relation until the filaments have set to an adhesive bond.

The invention may be more readily understood from the following description of specific embodiments thereof and the accompanying drawings in which FIG. 1 illustrates three rollers positioned to carry out the initial steps of the invention and FIG. 2 illustrates diagrammatically an apparatus for carrying out the complete process of the invention.

In FIG. 1, A and B are two counter-rotating rollers of substantially the same diameter mounted on parallel axes and having a coating of tacky viscous liquid thermoplastic material on the curved surfaces, said material forming a short bridge between the rollers at their point of closest proximity P. With the rollers rotating in the directions shown by the arrows, the tacky viscous liquid thermoplastic material adhering to the surfaces of both A and B is stretched as the surfaces of A and B draw apart in rotating past point P. Filaments F of viscous liquid thermoplastic are drawn out and are carried towards the line TT which is the outside tangent common to the surfaces of the rollers A and B. Before the filaments reach the level of line TT they intersect the surface of the roller C and are deposited thereon or on whatever is covering the bottom surface of roller C. Contact with the surface breaks the fine filaments and the greater part of the length of the filaments is deposited on or adheres to the surface of C, which can be moving. As rotation of rollers A and B continues the ends of the filaments adhering thereto move past the points of contact of the tangent TT and are incorporated again into the coating of viscous liquid thermoplastic material on the roller surfaces. A suitable source of viscous liquid thermoplastic (not shown) supplies material to the surfaces of the rollers A and B to replace the material removed as filaments on roller C and maintains the bridge of material between rollers A and B. Roller C obviously must be placed by the outside common tangent of rollers A and B on the side where the curved surfaces of A and B are drawing away Oct. 31, 1972 1.. M. GERM AIN ADHESIVELY LAMINATED FLEXIBLE WEBS Original Filed Oct. 21, 1963,

rollers. Heating elements were mounted within these rollers to maintain them at a uniform elevated temperature (110 C.) while in use. A third roller about five inches (12.5 cm.) wide and four inches cm.) in diameter was mounted above the foregoing rollers on a parallel axis so that its circumference cut through the top outside common tangent of the first rollers. A web of 4% inch wide (123 cm.) single ply paper tissue having a basis weight between 10 and 11 lbs. per 3000 square foot ream, (i.e. between 16.4 and 17.9 grams per square meter), was mounted to travel from a supply roll, under the third roller in contact with the bottom part of the surface thereof where the latter traversed the common tangent of the heated rollers, through the nip between the third roller and a laminating roller where the Web was laminated with a second web of the same type of paper tissue, and thence to a wind-up roll. on which the laminated material was wound. The c0unter-rotating rollers and third roller were driven uniformly at a speed of 200 r.p.m., and the tissue web travelling in contact with the third roller at its peripheral speed thus moved at about 200 ft./min. (61 m./min.). A supply of a viscous liquid thermoplastic hotmelt adhesive was maintained on the circumferences of the counter-rotating rollers to form a bridge across the gap between them, and as the rollers rotated, filaments of the adhesive were drawn from the melt in the bridge and rose towards the web passing under the third roller above and were deposited on the web as it moved across the outside common tangent line of the counter-rotating rollers. The deposited filaments formed a faint track of adhesive, about the same width as that of the counter-rotating rollers, along the length of the travelling web as filaments were deposited thereon; as the second web of tissue was laminated to the first web immediately after deposition of the filaments while the latter were still tacky, the filaments formed an adhesive bond between the webs which was found to be far stronger than the individual webs themselves. The width of the adhesively bonded area of the laminated tissue was that of the track of adhesive. The thermoplastic hot-melt adhesive used was a graft copolymer of vinyl acetate and polyoxyethylene, made, as described in British patent specification 920,760, by graft copolymerizing vinyl acetate onto a polyoxyethylene polymer sold under the name Carbowax 4000 (trademark), the proportions of the vinyl acetate and polyoxyethylene in the copolymer being in the ratio 85:15. The specific physical properties of this particular thermoplastic graft copolymer made it particularly suitable for use as an adhesive in laminating paper tissue in that the copolymer was completely water soluble or water dispersible; hence any laminated tissue web containing some proportion of the adhesive, on having to be scrapped for some reason during manufacture, did not have to be discarded because of its adhesive content but could be repulped in a beater, in which the adhesive would dissolve out in the water, and the repulped material could then be formed into a new web of paper tissue in the usual way. The proportion of adhesive applied to the tissue in this example was calculated by (1) cutting a large number of small uniform size samples of the laminated tissue both from areas which were free of adhesive and areas which were adhesively bonded, i.e. which were totally within the width of the track of adhesive, (2) weighing the samples, (3) averaging the weights of the adhesivecontaining and adhesive-free samples, and (4) from the difference in the average weights of the samples, calculating the average weight of adhesive applied to the tissue along the width of the track of adhesive. By the foregoing measurements and calculation it was found that the amount of adhesive on the laminated tissue amounted to an average of about 17% by weight of the laminated tissue in the adhesively bonded area. From the foregoing figure and the known basis weight of the single tissue web, previously mentioned, it can be calculated that 1 1b. (453 gm.) of the adhesive applied as a A inch (12 mm.) band would bond a length of 15,000 feet (4580 meters) of tissue web. Despite the delicate nature and light weight of the paper tissue, the adhesive applied thereto in this example did not penetrate through the web, nor was it visible through the web, i.e. the adhesive did not strike through the web. Furthermore, from the feel of the laminated tissue it was not possible to detect, by hand, the location of the track of adhesive in the web, i.e. the bonded part of the tissue web had the same feel to the hand as the unbonded part because the small amount of adhesive did not noticeably or appreciably affect the flexibility, thickness or drape of the tissue web. The substantial identity of the adhesively bonded laminate with the adhesive-free portion of the laminate with regard to feel, as described above, is particularly significant and advantageous for the utilization of the laminated webs in such applications as paper table napkins and facial and toilet tissue, where uniform thickness, feel, and flexibility are desired.

In view of the fact that the adhesive bond between the webs in the foregoing example was far stronger than the individual webs themselves, it is apparent that an adhesive bond of lesser strength, requiring only a smaller proportion of adhesive by weight of the webs being laminated, would be adequate for many if not all such laminations; thus in lieu of a proportion of 17% of adhesive, by weight of the web material in the bonded part of the Web, a lower proportion, e.g. 10%, 5%, or even less, appears to be suitable for many purposes. The proportion of adhesive applied to the web could be adjusted by various means, for example by increasing the temperature of the viscous liquid thermoplastic adhesive in the bridge of viscous liquid thermoplastic from which the filaments are formed, rendering it less viscous and making the filaments finer.

Inasmuch as a laminated structure comprising a fragile paper tissue lamina secured to another lamina with adhesive, without the adhesive noticeably or appreciably affecting the feel of the laminated structure, appears to be a novel article of manufacture, the invention thus further consists of laminated structures comprising a lamina of paper tissue adhesively secured to another lamina by the process described in the foregoing and following examples. The invention further and more specifically consists of a laminated paper tissue structure consisting of at least two laminae of paper tissue adhesively secured to one another by the process described in the foregoing example.

EXAMPLE 2 In the manner described in the foregoing example, using the same weight of paper tissue, the same grade of thermoplastic hot-melt adhesive, and the equipment described above, a web of surgical gauze was laminated to a web of paper tissue to form a laminated web of gauze and paper tissue, the adhesive being applied to the paper tissue before lamination of the gauze thereto. The laminated product had the full tensile strength of the gauze and the full liquid absorbency of the paper tissue.

EXAMPLE 3 This example was carried out with the apparatus described in Example 1, and with the same thermoplastic graft copolymer of vinyl acetate and polyoxyethylene being supplied to the counter-rotating rollers which were at ambient room temperature instead of being heated as in Example 1; the thermoplastic graft copolymer was softened by addition thereto of a small proportion of benzene (under 25% by weight of the copolymer) which converted the thermoplastic from a stiff rubbery solid at ambient room temperature to a mobile viscous liquid. The rotation of the counter-rotating rollers drew filaments from the viscous liquid thermoplastic which filaments were deposited on a web of paper tissue moving under the third roller and formed a track of filaments along the length of the web as it moved under the third roller. The benzene content of the liquid thermoplastic was so low that it did not make any observable mark on the tissue Web, and the track of thermoplastic formed an adhesive bond between the tissue web and a second web of tissue laminated therewith. Due to its volatility the benzene gradually evaporated from the filaments so that the bond they formed between the tissue webs eventually became a strong as the bond formed in Example 1 by the same type of thermoplastic filaments formed from the thermoplastic at elevated temperature in the absence of any liquid softener.

Numerous modifications can be made within the scope of the invention, in varying from the specific embodiments described herein. For example, instead of being fed onto a pair of counter-rotating rollers, the viscous liquid adhesive can be applied to a pair of continuous travelling belts whose paths of travel form the sides of a V at the bottom of which the liquid adhesive is maintained as a bridge from which filaments of adhesive are drawn as the adjacent surfaces of the belts travel upwards. Such an arrangement permits the accommodation in the open end of the V of a relatively long arcuate path of travel for a fragile web of tissue backed by a segment of a roller which intercepts the upward travel of the tacky filaments of adhesive formed between the travelling belts. Similarly, counter-rotating rollers, e.g. A and B in FIGS. 1 and 2, may not both necessarily be of circular cross-section. Thus roller A may have a cross section roughly rectilinear, e.g. triangular, square, hexagonal, with rounded corners and a radius of rotation approximately the same as the radius of the round roller it replaces. With such arrangement, bridging of the adhesive occurs only from the rounded corners of the roller A and filaments of adhesive are drawn out between the rollers only periodically during their rotation, instead of continuously. In this way a discontinuous track of adhesive filaments can be deposited along a continuous web moving in a path to intercept filaments formed between the rollers. Numerous other modifications and variations in the specific expedients described can be made Without departing from the invention the scope of which is defined in the following claims.

What is claimed is:

1. A laminated structure comprising a lamina of paper tissue adhesively secured to a second flexible lamina by short, fine, aligned filaments of flexible thermoplastic adhesive material, said filaments being suificiently fine to preclude their penetration through the paper tissue and the amount of adhesive between the laminae being sufficiently small to preclude it noticeably or appreciably affecting the flexibility, thickness, or drape of the combined laminae.

2. A laminated structure as claimed in claim 1, consisting of at least two laminae of paper tissue.

3. A laminated structure as claimed in claim 1, consisting of paper tissue laminated to a Web of surgical gauze.

References Cited UNITED STATES PATENTS 1,906,671 5/1933 Thunert 161--148 2,834,703 5/1958 Atkinson 161--l46 3,501,368 3/1970 Schabert et a1 l61148 3,502,538 3/1970 Petersen l61l50 WILLIAM J. VAN BALEN, Primary Examiner U.S. Cl. X.R. 

